These studies are directed at utilizing specific cloned virulence gene regions of Shigella as DNA probes or their sequence information in polymerase chain reaction assays to detect Shigella in stools. Our early studies showed that DNA probes were very sensitive, quick, and effective in detecting Shigella in the stool of diarrheal disease patients in Peru. In more recent studies utilizing polymerase chain reaction analysis of stools of healthy (i.e. asymptomatic) nonhuman primates and their healthy human caretakers, we have found a high rate of chronic, low level( i.e. below bacteriologic detection) asymptomatic carriage of Shigella. Our specific objectives are to determine (1) if these Shigella have full virulence potential,(2) the exact state in which Shigella are residing in these carriers( e.g. inside mucosal epithelial cells in the colon?), (3) the immune status of the carrier to Shigella, and (4) if this chronic low level carrier state is responsible for maintaining Shigella endemicity in the U.S. where there are now over 25,000 cases per year.